(1) Field of the Invention
The present invention relates to a synchronization preamble structure for the synchronization of a receiver of a OFDM transmission. The invention furthermore relates to an OFDM transmitter as well as to a method for the synchronization of a receiver of an OFDM transmission system.
(2) Description of Related Art
A synchronization preamble structure as shown in FIG. 1 is known. This known synchronization preamble structure can be subdivided in a A-FIELD, B-FIELD and a C-FIELD. The A-FIELD and the B-FIELD are subdivided in further parts. Each of the A-FIELD and the B-FIELD and the C-FIELD is designed to have an optimized special synchronization function at the receiving side. The A-FIELD for example serves for a coarse frame detection and an automatic gain control (AGC). The B-FIELD serves as a coarse frequency offset and timing synchronization. The C-FIELD serves for a channel estimation and fine synchronization.
Details about the concrete structure and generation of the B-FIELD can be found in the European patent application 99 103 379.6 in the name of Sony International (Europe) GmbH, which is to be regarded as representing prior art according to article 54(3) EPC. Regarding the details of the B-FIELD and generally the generation of the time domain synchronization preamble signal as shown in FIG. 1 reference is made to said prior non-prepublished application.
The symbols of the C-FIELD, which is generally of minor interest for the present invention, are defined in frequency domain asC64−26 . . . 26={1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,0, 1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1,1}The symbols B16 of the B-FIELD are short OFDM symbols, of which the subcarriers +−4, +−8, +−12, +−16, +−20, +−24 are modulated. The content in the frequency domain is equal to the one proposed in the above-cited EP-99 103 379.6. It can be defined asB−26 . . . 26=sqrt(2)*{0,0,1+j,0,0,0,−1+j,0,0,0,−1−j,0,0,0,−1−j,0,0,0,−1−j,0,0,0,1−j,0,0,0, 0,0,0,0,1−j,0,0,0,1−j,0,0,0,−1j,0,0,0,−1j,0,0,0,1+j,0,0,0,1+j,0,0}
The last repetition of the B-FIELD and the time domain, which is called IB16, is a sign inverted copy of the preceding B16. Note that the symbol sequence mapped onto subcarriers to generate B16 has particularly advantages for a low PAPR (peak-to-average-power-ratio) and small dynamic range.
According to the known concept as shown in FIG. 1 the symbols A16 of the A-FIELD are short OFDM symbols, of which the subcarriers +−2, +−6, +−10, +−14, +−18, +−22 are modulated (for a 64 point IDFT or IFFT). The content in the frequency domain can be defined asA1626 . . . 26=sqrt(2)*{0,0,0,0, +1+j,0,0,0,−1+j,0,0,0,−1−j,0,0,0, +1−j,0,0,0, +1+j,0,0,0, +1−j,0,0,0, +1+j,0,0,0, +1−j,0,0,0, +1+j,0,0,0, +1−j,0,0,0,−1−j,0,0,0,−1+j,0,0,0,0}The sign reversal of every second A16 symbol in the time domain is automatically achieved by the specified subcarrier loading. The last repetition of the A-FIELD in time domain, which is called IA16, is a copy of the preceding RA16.